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random: provide notifier for VM fork

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Drivers such as WireGuard need to learn when VMs fork in order to clear
sessions. This commit provides a simple notifier_block for that, with a
register and unregister function. When no VM fork detection is compiled
in, this turns into a no-op, similar to how the power notifier works.

Cc: Dominik Brodowski <linux@dominikbrodowski.net>
Cc: Theodore Ts'o <tytso@mit.edu>
Reviewed-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>
This commit is contained in:
Jason A. Donenfeld 2022-03-01 20:22:39 +01:00
parent 5acd35487d
commit f3c2682bad
2 changed files with 20 additions and 0 deletions
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15
drivers/char/random.c
View File

@ -1140,6 +1140,8 @@ void add_bootloader_randomness(const void *buf, size_t size)
EXPORT_SYMBOL_GPL(add_bootloader_randomness);
#if IS_ENABLED(CONFIG_VMGENID)
static BLOCKING_NOTIFIER_HEAD(vmfork_chain);
/*
* Handle a new unique VM ID, which is unique, not secret, so we
* don't credit it, but we do immediately force a reseed after so
@ -1152,10 +1154,23 @@ void add_vmfork_randomness(const void *unique_vm_id, size_t size)
crng_reseed(true);
pr_notice("crng reseeded due to virtual machine fork\n");
}
blocking_notifier_call_chain(&vmfork_chain, 0, NULL);
}
#if IS_MODULE(CONFIG_VMGENID)
EXPORT_SYMBOL_GPL(add_vmfork_randomness);
#endif
int register_random_vmfork_notifier(struct notifier_block *nb)
{
return blocking_notifier_chain_register(&vmfork_chain, nb);
}
EXPORT_SYMBOL_GPL(register_random_vmfork_notifier);
int unregister_random_vmfork_notifier(struct notifier_block *nb)
{
return blocking_notifier_chain_unregister(&vmfork_chain, nb);
}
EXPORT_SYMBOL_GPL(unregister_random_vmfork_notifier);
#endif
struct fast_pool {

5
include/linux/random.h
View File

@ -32,6 +32,11 @@ extern void add_hwgenerator_randomness(const void *buffer, size_t count,
size_t entropy);
#if IS_ENABLED(CONFIG_VMGENID)
extern void add_vmfork_randomness(const void *unique_vm_id, size_t size);
extern int register_random_vmfork_notifier(struct notifier_block *nb);
extern int unregister_random_vmfork_notifier(struct notifier_block *nb);
#else
static inline int register_random_vmfork_notifier(struct notifier_block *nb) { return 0; }
static inline int unregister_random_vmfork_notifier(struct notifier_block *nb) { return 0; }
#endif
extern void get_random_bytes(void *buf, size_t nbytes);